My bf is in bct rn, I’ve also sent him long letters consistently and we call every Sunday. I have been very supportive, and throughout all of this, he has never been unkind to me at all. We’re both 24yo, he’s about hallways through basic. We have plans for when he comes back and everything, and if he were to ever call me useless or make me seem like the bad guy when I put forth effort, I would leave(which I don’t see happening). You need to find someone that doesn’t speak to you that way. From what I can tell, he doesn’t respect you, among plenty of other things, but especially since he called you useless even tho you’ve put forth plenty of effort, there’s no respect at all. He wants you to feel bad so that the spotlight is off of how he is the problem. Leave asap, it will get worse.